Conventionally laminates are used in large quantities for packaging and dispensing of various products, including personal care and food products. The laminates are usually made of plastic polymers because of the inherent properties, such as physical properties of strength, light weight, durability, non-toxicity, resistance to light and heat, and inertness towards chemicals. Such properties make laminates an appropriate choice for application in packaging industry.
Metallized polymer laminates are laminates with a thin layer of a metal deposited or coated on the surface of a polymer layer. This metallization of laminates imparts a glossy metallic appearance at a reduced weight. Further, metallized films provides barrier for protection against elements including light, water, moisture and gases. Metallized polyester and BOPP are commonly known in the flexible laminate manufacturing industry. These laminates are usually formed by using one of the components as a metallized layer and bonded to the sealant layer using solvent-based or solvent-less adhesives.
Biaxially oriented polypropylene (BOPP) films are widely used as films for packaging, since they are excellent in moisture barrier properties, strength, clarity and surface gloss, and it is also widely practiced to metalize them by a metal such as aluminum, for the purposes of making them look better because of the metallic gloss when displayed, improving the gas barrier properties, and inhibiting the deterioration of the packaged product otherwise caused by external light such as ultra violet light from sun light rays.
However since the surface of a BOPP film is inactive, it is generally practiced to activate the surface by such treatment as corona discharge treatment or flame treatment, for improving the adhesion between the metallic film and the base material film at the time of metallization.
U.S. Pat. No. 4,297,187 discloses corona discharge treatment in a mixed gas consisting of nitrogen and carbon dioxide. However, in the corona discharge treatment method, a higher treatment intensity can activate the surface more and improves the adhesive strength between the metallic film and the surface layer of the base material film, but it is known that, at the same time, the base material is deteriorated and therefore that the surface layer of the base material film is likely to be delaminated from the inside of the base material film.
U.S. Pat. No. 6,190,760 discloses a biaxially oriented polypropylene film to be metallized including a surface layer made of a polypropylene resin with the endothermic main peak by crystal fusion in a range of 155 deg C. to 163 deg C. and with a heat of crystal fusion 20 to 90 m J/g, being laminated layer at least one side of the base layer made of isotactic polypropylene; and the wetting tension of the surface layer, being 33 to 55 Mn/M. U.S. Pat. No. 6,190,760 also discloses a metallized biaxially oriented polypropylene film, including a thin metallic film, being laminated on the surface layer said biaxially oriented polypropylene film to be metallized. U.S. Pat. No. 6,190,760 also further discloses a laminate obtained by using said metallized biaxially oriented polypropylene film. US 2011/0274892 discloses biaxially oriented film including bio based polyolefin which is derived from non-petroleum sourced monomers. US 2011/0274892 also discloses a laminate film including at least one bio-based polyolefin layer including at least 53 pMC of radiocarbon (14C) content. The laminate film may include additional layers such as a second bio-based polyolefin resin-containing layer of at least 53 pMC radiocarbon content, and a metal layer.
Metallized polymer films are widely used for food packaging and also for decorative purposes. US2008/0226854 describes metallized films with metal layers coated on one or more ethylene acid copolymers, with another thermoplastic layer. The prior arts discussed are incorporated in its entirety herein by reference.
In the packaging industry, metallized films are preferred as it enhances the shelf life and appeal of the packaged product. Metallized films have become a good replacement of metal cans, glass or rigid structures in packaging, the requirement of barrier materials and coex structures.